1. Technical Field
The invention relates to the field of metal fibre filters, filtration systems in which such filters are used; and the use of such filters and filtration systems, e.g. in hot gas filtration, in oil slurry filtration or in liquid filtration.
2. Background Art
Filtration systems are known in which the filter medium is provided by sintered metal powders. However the level of porosity that can be obtained with such sintered metal powders is too low for many applications. Sintered metal fibre filters have higher porosity levels and therefore a much better filtration performance. Hence sintered metal fibre filters are preferred solutions for many applications.
The method of manufacturing of sintered metal powder filters and of metal fibre filters is totally different. Metal powder can be provided in the shape of the final filter in a mould. If required, appropriate reinforcing means (such as metal screens or metal meshes) can be positioned in the mould as well. Subsequently, the whole is sintered into shape. Metal fibre filters need to be manufactured in a different way. Metal fibres are provided in two-dimensional fibre webs. Reinforcing layers (e.g. metal meshes) can be added. Such a stack can be sintered into a two dimensional plate structure that can be shaped afterwards, e.g. into a cylindrical structure wherein the seam is welded.
Sintered metal fibre filters are used in filtration systems, e.g. for filtration of hot gas, for liquid filtration or for filtration of oil slurries. In existing systems, the metal fibre filters (which can include one or more reinforcing layers such as meshes or expanded steel sheets) are supported over the surface of the filter by e.g. a welded metal wire structure (mostly a cage like structure, e.g. a cylindrical cage in the case of cylindrical filters).
An example is a filter assembly with a tubular or cylindrical filter element (comprising a sintered metal fibre web) and a cylindrical perforated core (e.g. a cylindrical structure made from metal wires in longitudinal and circumferential direction and which are welded at their contacting points). The cylindrical filter element is formed around the cylindrical perforated core. Both the cylindrical filter element and the cylindrical perforated core are affixed at their ends to end caps, e.g. by brazing, welding or gluing. It is a problem of such filtration systems that failure can occur after multiple back pulse cleaning of such filters.